CONTROL AND METHODS FOR PV INVERTER MINIATURIZATION
Analytics
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Abstract
Analyzing the price of PV generation systems in different market sectors shows that the portion of inverter cost and Balance of System (BoS) are increased due to advent of new PV module technologies and dramatic cost reduction in PV module production in recent years. The BoS cost for residential PV systems changed from 15% to 24% between the 2009 and 2012. The same trend can be seen in other power level sectors such as commercials and utility level PV generations. After 2012, due to investment on new PV inverter architectures the BoS cost share reduced to 20% at beginning of 2016, but still there is a large room for improvement. Therefore, it is critical to come up with an architecture that can revolutionize the PV generations in different power levels, to reduce the inverter cost and BoS costs.The available grid-tied PV inverter technologies can be classified in two main categories such as central PV inverter systems and module-integrated PV inverter systems. However, the balance of system and inverter cost are still a major part of PV inverter systems’ cost. The main goal of this dissertation is to design and implement a decentralized control scheme for the grid-tied AC-stacked PV inverter architecture which is expected to be more cost effective than others due to different cabling structure, connection and physical implementation of the system. The Decentralized control scheme allows the inverter miniaturization, because there is no need for wideband communications. In addition, this architecture because of lower counts of components, has the potential to be miniaturized and have high power density if it can be implemented in a decentral manner. This dissertation will study this architecture for the first time and analyze the feasibility and stability of decentralized Hybrid Current/Voltage-mode Control (HCVC) scheme for this architecture with minimum communication requirements using the Relative Gain Array (RGA) approach. Based on RGA analysis, it is shown for the first time that a fully decentralized control architecture with no communication between inverters can regulate the output power properly and generate the maximum power from PV modules with minimum mismatch losses. Moreover, novel grid integration and smart inverter functions such as reactive power support and background harmonics mitigation, are designed and implemented and analyzed for this architecture. The reactive power control method and background harmonics mitigation methods introduced in this thesis have the main advantage of maximizing the operation margin for increasing the system stability during nominal operating condition and during disturbances such as partial shading, gird voltage sag and swell and frequency disturbances. Controller robustness analysis and evaluating the impact of components inaccuracies on robust operation of this decentralized control scheme are also provided in this dissertation. Robustness analysis is crucial, especially for distributed architectures where subsystems are regulated with local measurements. The Smart Inverter Robustness Index (SIRI) is introduced as a comprehensive tool for evaluating the robust operation of grid-tied PV inverter systems and the impact of component inaccuracies on robustness of AC-stacked PV inverter system is studied.The proposed control methods and architectures in this research have been verified using mathematical modeling and analysis, off-line simulation in Matlab/Simulink, Controller Hardware-in-the-Loop (CHiL) and lab-scale experimental setup. All prove the effectiveness of proposed methods during symmetrical conditions, asymmetrical conditions and fault conditions.